Are these returns adequate? (pictures)

[Wizzard of Oz]

You need the installer to come out and check several items. First is system static, which is the resistance to air flow through the duct system. My guess is your static is high, which reduces the total CFM your system delivers. We've already established your returns are undersized, by my ductulator your getting around 1300 to 1400 CFM and a 5 Ton system needs 2000 CFM. The reason NOT to use pleated filters at this point is they are more restrictive and will reduce your air flow further, wait until your contractor has corrected the issue (maybe add another return or upsize existing ones). Second is what is controling your dual fuel? Is it a control board or just the T-stat? There are different air flow requirements for a heat pump and a gas furnace, so some of your problem could be the blower speed when the heat pump is running. Third is temperature rise, you can get and idea from return to supply. Lastly I believe bobb25 is looking for duct loss that's why you'd look at temp at the unit then out at each of the registers. This would contribute to the temperature difference from room to room. Bottom line is your contractor needs to take another look at these issues...Good Luck

[CaptainKangaroo]

I've solved many problems for customers by telling them to get rid of those pleated filters. Does your system work ok with El Chepo brand filters? If you don't have any, how does it work without any filters?.

By El Cheapo, do you mean the fiberglass type? I'll give them a try. Since we were remodeling, I tried to keep high-quality, fresh filters installed to prevent construction dust from getting into the brand-new system. The construction is over now, so I'm not as concerned about the dust. Do you know where I could find information on airflow of various filter types? Is that sort of information available?

You really need to get an HVAC contractor, and not the guy who installed it.

I'm willing to work with the installer as long as he is willing to work with me. I have already invested quite a lot of money into this system.

[CaptainKangaroo]

Second is what is controling your dual fuel? Is it a control board or just the T-stat? There are different air flow requirements for a heat pump and a gas furnace, so some of your problem could be the blower speed when the heat pump is running.

I don't really know what controls the dual fuel, though I suppose it's a combination of both the thermostat (Honeywell TH8000) and the system (Maytag M1200). The system has a variable speed blower and some switches on the control board that are available for fine-tuning. I have not adjusted anything yet. The manual makes the following statement regarding the switch settings:

"The CFM values listed in the tables are not dependent on duct static pressure. The motor automatically compensates for changes in duct statuc pressure (within the limits of the motor)."

I suppose my system is outside of the limits of the motor.

Third is temperature rise, you can get and idea from return to supply. Lastly I believe bobb25 is looking for duct loss that's why you'd look at temp at the unit then out at each of the registers. This would contribute to the temperature difference from room to room. Bottom line is your contractor needs to take another look at these issues...Good Luck

I'll measure the temperature at the return and at various registers tonight. What kind of number am I looking for? I assume it is different for heat pump vs. gas.

Thanks

[beenthere]

Thoise 3M filtretes are about the worst filter you could be using for air flow.

Also, the higher the static pressure a VS blower has to work against, the more electric it uses.

[skippedover]

We've been told to keep the doors open at all times, but this doesn't always work. Some folks, especially seniors and infants have been complaining of headaches, asthma, breathing difficulties, etc.

How do we start remedying this? Do we get someone in to test our ventilation? Do we go about possibly seeing if we can install additional returns in the bedrooms where people are complaining? Any help would be appreciated.

You need a whole house analysis done on several of the units. Blower door testing is the best way to start the process. www.comfortinstitute.org is a good place to start.

[CaptainKangaroo]

Like already said two 12 inch ducts are not big enough and to make matters worse just by looking at that last picture I can tell you aren't even getting a full 12 inches.

Apparently the concept of perspective is something I need to learn. The first duct is 16", not 12". I had estimated the width based on the width of the hole in the floor, which I had measured. Of course, the duct opening is several inches below the hole, and I neglected to take that into account when I estimated. I went back to the return and managed to reach in far enough to measure, and the duct is actually 16".

In area, the duct is about 200sq.in., and the hole cut in the floor is less than 140sq.in. (after subtracting the width of the joist). So, I would think that the hole needs to be larger.

For a return, what CFM can a 16" return duct accomodate? Assuming I enlarge the hole in the floor, should a 16" and a 12" return duct be sufficient?

Sorry for the misinformation. Thanks for all the great advice!

[beenthere]

How much depends on the TEL it is, and the restriction of the grille, and the hole in the floor.

How long are the return runs, how many turns, how are they tapped into the furnace.

[CaptainKangaroo]

How much depends on the TEL it is, and the restriction of the grille, and the hole in the floor.

How long are the return runs, how many turns, how are they tapped into the furnace.

Ok, one more stupid question: what is TEL?

The 16" return duct is closest to the blower; maybe 15 feet or so.

Thanks

[beenthere]

Total
Equivalent
Length

If you have a standard blower you could be getting 1200 CFM through it.(WAG) Provided the supplies aren't too restrictive.

[Wizzard of Oz]

I don't really know what controls the dual fuel, though I suppose it's a combination of both the thermostat (Honeywell TH8000) and the system (Maytag M1200). The system has a variable speed blower and some switches on the control board that are available for fine-tuning. I have not adjusted anything yet. The manual makes the following statement regarding the switch settings:

"The CFM values listed in the tables are not dependent on duct static pressure. The motor automatically compensates for changes in duct statuc pressure (within the limits of the motor)."

I suppose my system is outside of the limits of the motor.



I'll measure the temperature at the return and at various registers tonight. What kind of number am I looking for? I assume it is different for heat pump vs. gas.

Thanks

The typical limit for variable speed blower motor is .8 inches water column total system static, beyond that they begin to pulse and behave irradically.

The heat rise depends on the unit but gas heat is usually between 30 to 50. A heat pump is 20-30, however in low abient conditions this will be less.

Your 12 inch duct should pull about 650 cfm and a 16 should be 1400, so the total is 2050 IF your getting proper air flow through the one that looks like it is restriced off the boot box. The bare minimum. Again this can be verified buy checking the static, the values are at .1 iwc per run so your looking for a .2 on the return side to deliver that cfm. your total static (both return and supply) should be .5 iwc.

I'm still curious as to what is controlling your staging for your "duel" fuel use. Does your TH8000 (I'm assuming you actually have a TH8320) have an outdoor sensor or an external fossil fuel kit? As I recall both your gas and electric energy usage is higher. If staging is the only control then thats going to contribute to the energy costs, as your heat pump will be first stage which under low ambient conditions won't give enough temperature rise, so then the second stage (gas) kicks in and satisfy the stat. If it has an outdoor sensor then it can lock out the heat pump from operating below a selected temperature and allow gas to heat the home.

Hope this helps and doesn't confuse the matter more

[beenthere]

wizard, your confusing FR, with static pressure.

[CaptainKangaroo]

The heat rise depends on the unit but gas heat is usually between 30 to 50. A heat pump is 20-30, however in low abient conditions this will be less.

Do you mean that the air temperature at a register should be 20-30 degrees F higher than the air at the return grill when the heat pump is running? I need to check again, but I am pretty sure it is nowhere near that. I measured the air at the register in the room that we have been having trouble heating, and it was around 76 while the return was at 65. That's only 11 degrees. I need to repeat this at various registers; this was at the register farthest from the blower.

I also did a quick test of the gas heat. I put the tstat on emergency heat and after 5 minutes or so the air temperature at the same register was 100F.

Your 12 inch duct should pull about 650 cfm and a 16 should be 1400, so the total is 2050 IF your getting proper air flow through the one that looks like it is restriced off the boot box. The bare minimum. Again this can be verified buy checking the static, the values are at .1 iwc per run so your looking for a .2 on the return side to deliver that cfm. your total static (both return and supply) should be .5 iwc.

I am going to ask my installer to perform these measurements. I think I remember reading on the forums that if you measure the static pressure at the blower, you can use a chart from the manufacturer to determine the CFM? I have the installation manual for the unit, but the only charts are for the coolant charge. Where do you get the static pressure -> CFM chart?

I'm still curious as to what is controlling your staging for your "duel" fuel use. Does your TH8000 (I'm assuming you actually have a TH8320) have an outdoor sensor or an external fossil fuel kit? As I recall both your gas and electric energy usage is higher. If staging is the only control then thats going to contribute to the energy costs, as your heat pump will be first stage which under low ambient conditions won't give enough temperature rise, so then the second stage (gas) kicks in and satisfy the stat. If it has an outdoor sensor then it can lock out the heat pump from operating below a selected temperature and allow gas to heat the home.

Hope this helps and doesn't confuse the matter more

You are correct, it is actually a TH8320U. It does have an outdoor temperature sensor, and the compressor lockout is set to 35 degrees. (Actually that is not very accurate because the outdoor sensor temperature tends to slowly rise as the unit runs, so I've seen the heat pump running when the actual outdoor temperature was 30 or less. I posted about this issue in another thread: http://www.hvac-talk.com/vbb/showthread.php?t=163741.)

Thanks

[Wizzard of Oz]

Yes I'm refering to the temp from return to supply. Your 35 degrees in gas seems in the ballpark, and I think the Maytag M1200 is two stage gas so this is probably first stage gas. The 11 degrees in heat pump mode seems a little low depending on the outdoor ambient. We typically see 20 degrees here in Arizona down to the mid 30's. Measure your other duct runs and see if there's a big (5-10 degrees) difference, if there is it could indicated an issue with the duct run (either leakage, or improper insulation). If your installer is coming out you might have him double check the refrigerant too.
Thanks beenthere I did got confused on the FR and static, I was putting some black gas pipe together as I wrote, and must have gotten to close the the thread sealant.
The system static is obtained by using a magnehelic and measuring the duct pressure in both the supply and return. This should be somewhere between 0.5 to 0.8 w.g. if it's higher it could indicate a restriction in the ductwork. This value on a standard blower can be used to determine the cfm output from the blower motor performance charts. On a variable as stated before it works against the static to deliver a specific cfm so were just look to see if the static is within the motors operating range.
I read the thread on your outdoor sensor, and it sounds like it's either in a bad location or is malfunctioning. The outdoor ambient should not raise because the H/P is on. This is consistant with your observation the the H/P was running at 30 when the lock out is set for 35. You might try bumping thelockout to 40 degrees and see what that does. It also sounds like several other pros have had problems with it too. If you cannot get it dialed in using that set up you might consider either the Honeywell Fossil Fuel Kit or a Lennox FM21, to control your dual fuel issue.
Anyone got other ideas?